Conventionally, as a stereophonic sound field reproducing apparatus, for example, the OSS (Ortho-Stereophonic System) which was suggested by Tomotoshi Miura (professor at the general research institute, Tokyo Denki University) is known. FIG. 18 is an explanatory diagram showing a structure of the conventional OSS. This OSS has a dummy head 51 called as HATS (Head and Torso Simulator) arranged in a stereophonic sound field 50 as recording target, a minimicrophone 52L arranged in a position of tympanic membrane of a left ear inside the HATS 51, a minimicrophone 52R arranged in a position of tympanic membrane of a right ear inside of the HATS 51. There is an OSS-Network section 60 for inputting signals from the minimicrophones 52L and 52R and executing a cross talk canceling process. A speaker 71L is provided in front-left of a listener (user) 72. A speaker 71R is provided in front-right of the user 72. The OSS reproduces the stereophonic sound field 70.
The OSS-Network section 60 has circuits 61L and 61R for correcting a free sound field front incident head transmission function of the user 72, a cross talk canceling circuit 62L for outputting a cross talk canceling signal to be added to a signal to the speaker 71R, a cross talk canceling circuit 62R for outputting a cross talk canceling signal to be added to a signal to the speaker 71L, a mixing circuit 63L for adding a cross talk canceling signal to a signal to the speaker 71L, a mixing circuit 63R for adding a cross talk canceling signal to a signal to the speaker 71R, a circuit 64L for correcting a characteristic between the speaker 71L and the user 72 according to an inverse function, and a circuit 64R for correcting a characteristic between the speaker 71R and the user 72 according to an inverse function.
How the conventional OSS works will be explained here. At first, the HATS 51 arranged in the stereophonic sound field 50 as recording target executes binaural recording. A sound, which was measured by the minimicrophone 52L arranged in the position of the tympanic membrane of the left ear in the HATS 51, and a sound, which was measured by the minimicrophone 52R arranged in the position of the tympanic membrane of the right ear in the HATS 51, are converted into signals L and R respectively. The signals L and R are input into the OSS-Network section 60.
The signals L and R input into the OSS-Network section 60 are corrected by the circuits 61L and 61R for correcting a free field front incident head transmission function of the user 72. These corrections are represented by:EL=HEL/DELER=HER/DER.Here, EL is a transmission function of the circuit 61L, ER is a transmission function of the circuit 61R, HEL/DEL and HER/DER are correction terms of the free field front incident head transmission function.
Next, the cross talk canceling circuit 62L inputs an output signal of the circuit 61L and outputs a cross talk canceling signal to be added to a signal to the right speaker 71R. Similarly, the cross talk canceling circuit 62Rinputs an output signal of the circuit 61R and outputs a cross talk canceling signal to be added to a signal to the left speaker 71L. A transmission function CL of the cross talk canceling circuit 62L and a transmission function CR of the cross talk canceling circuit 62R are represented by:CL=−HLO/HLSCR=−HRO/HRS.Here, HLO is a characteristic between the left speaker 71L and the right ear of the user 72, HLS is a characteristic between the left speaker 71L and the left ear of the user 72, HRO is a characteristic between the right speaker 71R and the left ear of the user 72, and HRS is a characteristic between the right speaker 71R and the right ear of the user 72.
Next, the mixing circuit 63L mixes the output signal of the circuit 61L with the cross talk canceling signal from the cross talk canceling circuit 62R so as to output the mixed signal to the circuit 64L. Similarly, the mixing circuit 63R mixes the output signal of the circuit 61R with the cross talk canceling signal from the cross talk canceling circuit 62L so as to output the mixed signal to the circuit 64R. The circuits 64L and 64R process the input signals according to the inverse functions for correcting the characteristics between the speakers 71L and 71R and the user so as to output the processed signals to the speakers 71L and 71R. A transmission function TL of the circuit 64L and a transmission function TR of the circuit 64R are represented as follows:TL=1/((1−CL×CR)HLS) TR=1/((1−CL×CR)HRS).
The signals processed in the OSS-Network section 60 are reproduced from the reproduction-use right and left speakers 71L and 71R, and the stereophonic sound field 70 is reproduced. HLS, HLO, HRS, HRO, HEL, HER, DEL and DER are previously measured, and characteristics (filter factors) of the respective circuits in the OSS-Network section 60 are determined.
However, in the conventional OSS, since a positional relationship between the head of the user and the speakers is not fixed, it is necessary to fix a position of the user. When the user moves his/her head, there arises a problem that the user feels that sound quality is incongruous or a phase is inverted.